Linear polyesters such as poly(alkylene terephthalates) are well known commercially available polymers. They have many valuable characteristics including strength, toughness, high gloss and solvent resistance. Linear polyesters are conventionally prepared by the reaction of a diol with a functional derivative of a dicarboxylic acid, typically a diacid halide or ester. Further, the above-described polyesters may be fabricated into articles by a number of well known techniques including injection and roto molding and extrusion.
In recent years, macrocyclic polyester oligomers have been developed and desired since they have unique properties which make them attractive as matrices for polymer composites. Such desired properties stem from the fact that macrocyclic polyester oligomers exhibit low viscosities, allowing them to impregnate a dense fibrous preform easily. Furthermore, such macrocyclic polyester oligomers melt and polymerize at temperatures well below the melting point of the resulting polymer. Thus, melt flow, polymerization and crystallization can occur isothermally and, therefore, the time and expense required to thermally cycle a tool is favorably reduced.
Methods for producing macrocyclic polyester oligomers typically result in the formation of impurities which often interfere with the polymerization of the macrocyclic polyester oligomers as well as their valuable characteristics. Such impurities are often polar and include alkanediols and monomers, dimers and linear oligomers, all of which are often hydroxy or amine terminated. It is of increasing interest, therefore, to isolate macrocyclic polyester oligomers from such impurities.
The instant invention is directed to a process for isolating macrocyclic polyester oligomers from impurities by contacting solutions of macrocyclic polyester oligomers with molecular sieves.